Method and system for purifying a caustic fluid including sulfur

ABSTRACT

Methods and systems for purifying a caustic fluid including sulfur are provided.

BACKGROUND OF THE INVENTION

In a mercaptan removal system, disulfide oil (DSO) in a caustic streamis carried back to the final hydrocarbon product which can includepropane, butane, liquid petroleum gas (LPG), fuel gas, naptha, orgasoline, resulting in an increased sulfur content, such that the sulfurcontent of the product exceeds the target specification.

There is a need for an improved system and method for removing sulfurfrom the caustic stream.

The present invention provides for ameliorating at least some of thedisadvantages of the prior art. These and other advantages of thepresent invention will be apparent from the description as set forthbelow.

BRIEF SUMMARY OF THE INVENTION

An aspect of the invention provides a method for purifying a causticfluid including sulfur, the method comprising: (a) mixing a causticfluid including sulfur with a hydrocarbon solvent, including injectingthe hydrocarbon solvent, at a pressure greater than a pressure of thecaustic fluid including sulfur, at a rate in the range of 3% to 10% of aflow rate of the caustic fluid including sulfur into a mixing valveoperated at a pressure differential across the mixing valve in the rangeof 10 psid to 50 psid; (b) passing the caustic fluid including sulfurmixed with hydrocarbon solvent at a temperature in the range of from 50°F. to 150° F. through a prefilter assembly operated at a pressuredifferential in the range of 1 psid to 25 psid, the prefilter assemblycomprising a housing including the inlet and an outlet and defining afluid flow path between the inlet and the outlet with at least oneporous prefilter element in the housing across the fluid flow path,providing a solids-depleted caustic fluid including sulfur mixed withhydrocarbon solvent; (c) passing the solids-depleted caustic fluidincluding sulfur mixed with hydrocarbon solvent at a temperature in therange of from 50° F. to 150° F. through the inlet of a liquid-liquidcoalescer assembly comprising a liquid-liquid coalescer assembly housingincluding the inlet and at least one liquid-liquid coalescer filterelement in the liquid-liquid coalescer assembly housing, theliquid-liquid coalescer assembly housing having an upper part having anupper port, and a lower part having a lower port, wherein theliquid-liquid coalescer assembly is operated at a pressure differentialin the range of 1 psid to 15 psid with a flow rate in the range of 10gpm to 50 gpm per liquid-liquid coalescer filter element; (i) passingcoalesced droplets comprising sulfur and hydrocarbon solvent through theupper port; and (ii) passing purified caustic fluid having a reducedsulfur content though the lower port.

In one aspect of the method, (a) includes mixing a caustic fluidincluding sulfur having a caustic concentration in the range of 1 degreeBaume to 10 degrees Baume with the hydrocarbon solvent.

In a preferred aspect of the method, the caustic fluid including sulfurcomprises disulfide oil (DSO).

In another aspect, a system for purifying a caustic fluid includingsulfur, comprises: (a) a mixing assembly having at least a first inletport, a mixing valve, and an outlet port; (b) a first conduit forreceiving a caustic fluid including sulfur, the first conduit having afirst conduit first end in fluid communication with a source of thecaustic fluid, and a first conduit second end in fluid communicationwith the at least one inlet port of the mixing assembly; (c) a secondconduit for receiving a hydrocarbon solvent, the second conduit having asecond conduit first end in fluid communication with a source of thehydrocarbon solvent, and a second conduit second end in fluidcommunication with the first conduit; (d) a prefilter assemblycomprising a housing having a prefilter assembly inlet and a prefilterassembly outlet and defining a fluid flow path between the prefilterassembly inlet and the prefilter assembly outlet, and having at leastone porous prefilter element arranged in the prefilter assembly housingacross the fluid flow path, wherein the prefilter assembly inlet is influid communication with the outlet port of the mixing assembly, and theprefilter assembly outlet is in fluid communication with an inlet of aliquid-liquid coalescer assembly; (e) the liquid-liquid coalescerassembly comprising a housing including at least one liquid-liquidcoalescer filter element in the housing, the housing having theliquid-liquid coalescer assembly inlet, and an upper part having anupper port for receiving coalesced droplets comprising sulfur andhydrocarbon solvent, and a lower part having a lower port for receivingpurified caustic fluid having a reduced sulfur content.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The Figure is a drawing showing a schematic of a system according to anaspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

An aspect of the invention provides a method for purifying a causticfluid including sulfur, the method comprising: (a) mixing a causticfluid including sulfur with a hydrocarbon solvent, including injectingthe hydrocarbon solvent, at a pressure greater than a pressure of thecaustic fluid including sulfur, at a rate in the range of 3% to 10% of aflow rate of the caustic fluid including sulfur into a mixing valveoperated at a pressure differential across the mixing valve in the rangeof 10 psid to 50 psid; (b) passing the caustic fluid including sulfurmixed with hydrocarbon solvent at a temperature in the range of from 50°F. to 150° F. through a prefilter assembly operated at a pressuredifferential in the range of 1 psid to 25 psid, the prefilter assemblycomprising a housing including the inlet and an outlet and defining afluid flow path between the inlet and the outlet with at least oneporous prefilter element in the housing across the fluid flow path,providing a solids-depleted caustic fluid including sulfur mixed withhydrocarbon solvent; (c) passing the solids-depleted caustic fluidincluding sulfur mixed with hydrocarbon solvent at a temperature in therange of from 50° F. to 150° F. through the inlet of a liquid-liquidcoalescer assembly comprising a liquid-liquid coalescer assembly housingincluding the inlet and at least one liquid-liquid coalescer filterelement in the liquid-liquid coalescer assembly housing, theliquid-liquid coalescer assembly housing having an upper part having anupper port, and a lower part having a lower port, wherein theliquid-liquid coalescer assembly is operated at a pressure differentialin the range of 1 psid to 15 psid with a flow rate in the range of 10gpm to 50 gpm per liquid-liquid coalescer filter element; (i) passingcoalesced droplets comprising sulfur and hydrocarbon solvent through theupper port; and (ii) passing purified caustic fluid having a reducedsulfur content though the lower port.

In one aspect of the method, (a) includes mixing a caustic fluidincluding sulfur having a caustic concentration in the range of 1 degreeBaume to 10 degrees Baume with the hydrocarbon solvent.

In some aspects, the method is carried out at a system pressure in therange of 50 psig to 600 psig, e.g., to ensure that the hydrocarbonsolvent is maintained in a liquid state.

In a preferred aspect of the method, the caustic fluid including sulfurcomprises disulfide oil (DSO), in a more preferred aspect, the methodcomprises a mercaptan removal process.

In another aspect, a system for purifying a caustic fluid includingsulfur, comprises: (a) a mixing assembly having at least a first inletport, a mixing valve, and an outlet port; (b) a first conduit forreceiving a caustic fluid including sulfur, the first conduit having afirst conduit first end in fluid communication with a source of thecaustic fluid, and a first conduit second end in fluid communicationwith the at least one inlet port of the mixing assembly; (c) a secondconduit for receiving a hydrocarbon solvent, the second conduit having asecond conduit first end in fluid communication with a source of thehydrocarbon solvent, and a second conduit second end in fluidcommunication with the first conduit; (d) a prefilter assemblycomprising a housing having a prefilter assembly inlet and a prefilterassembly outlet and defining a fluid flow path between the prefilterassembly inlet and the prefilter assembly outlet, and having at leastone porous filter element arranged in the prefilter assembly housingacross the fluid flow path, wherein the prefilter assembly inlet is influid communication with the outlet port of the mixing assembly, and theprefilter assembly outlet is in fluid communication with an inlet of aliquid-liquid coalescer assembly; (e) the liquid-liquid coalescerassembly comprising a housing including at least one liquid-liquidcoalescer filter element in the housing, the housing having theliquid-liquid coalescer assembly inlet, and an upper part having anupper port for receiving coalesced droplets comprising sulfur andhydrocarbon solvent, and a lower part having a lower port for receivingpurified caustic fluid having a reduced sulfur content.

Aspects of the system further can comprise a first receptacle forreceiving coalesced droplets comprising sulfur and hydrocarbon solventpassing from the upper port of the liquid-liquid coalescer assembly, anda second receptacle for receiving purified caustic fluid having areduced sulfur content passing from the lower port of the liquid-liquidcoalescer assembly.

In some aspects of the system, the system is operable at a systempressure in the range of 50 psig to 600 psig.

In alternative aspects of the method and system, the liquid-liquidcoalescer assembly can include at least one porous prefilter elementarranged upstream of the at least one liquid-liquid coalescer filterelement in the liquid-liquid coalescer assembly housing (rather than, orin addition to, the separate prefilter assembly), wherein the at leastone porous prefilter element can be in the form of, for example, acartridge or a planar element.

Each of the components of the invention will now be described in moredetail below, wherein like components have like reference numbers.

Using the illustrated aspect shown in the FIGURE for reference, system1000 comprises: a mixing assembly 150 having at least a first inlet port101, a mixing valve 100, and an outlet port 102 (in the illustratedaspect a differential pressure gauge 175 is arranged across the mixingassembly); a first conduit 10 for receiving a caustic fluid includingsulfur, the first conduit having a first conduit first end 10 a in fluidcommunication with a source of the caustic fluid, and a first conduitsecond end 10 b in fluid communication with the at least one inlet portof the mixing assembly; a second conduit 20 for receiving a hydrocarbonsolvent, the second conduit having a second conduit first end 20 a influid communication with a source 50 of the hydrocarbon solvent, and asecond conduit second end 20 b in fluid communication with the firstconduit (in the illustrated aspect a pump 22, a flow control valve 23and a flow meter 24 are interposed between the second conduit ends 20 aand 20 b; a third conduit 30 for receiving the mixed fluid exiting themixing assembly, the third conduit having a third conduit first end 30 ain fluid communication with the outlet port of the mixing assembly, anda third conduit second end 30 b in fluid communication with a prefilterassembly inlet 201 of a prefilter assembly 200 comprising a housing 210having the prefilter assembly inlet 201 and a prefilter assembly outlet202 and defining a fluid flow path 250 between the inlet and the outlet,and having at least one porous prefilter element (e.g., a porousprefilter cartridge) 251 arranged in the housing across the fluid flowpath, the prefilter assembly outlet in fluid communication, via a fourthconduit 40 having a first end 40 a and a second end 40 b, with aliquid-liquid coalescer assembly inlet 301 of a liquid-liquid coalescerassembly 300, the liquid-liquid coalescer assembly comprising a housing310 including at least one liquid-liquid coalescer filter element 351 inthe housing, and an upper part 360 having an upper port 361 forreceiving coalesced droplets comprising sulfur and hydrocarbon solvent,and a lower part 370 having a lower port 371 for receiving purifiedcaustic fluid having a reduced sulfur content, wherein the purifiedcaustic fluid can be passed from lower port 371 to, for example, amercaptan removal extractor.

In one preferred aspect, the system includes a collection sump 400communicating with the upper port 361, the sump receiving coalesceddroplets comprising sulfur and hydrocarbon solvent, wherein hydrocarbonextract can be passed from collection sump port 401 along fifth conduit50 having a first end 50 a and a second end 50 b via pump 62 andsubsequently, for distillation or hydrotreatment, via sixth and seventhconduits 60 and 70, or for recirculation, via eighth conduit 80 tosource 50 of the hydrocarbon solvent.

Suitable hydrocarbon solvents include, for example, naphtha, hexane,liquid propane and other hydrocarbon solvents with low sulfur content.

A variety of mixing assemblies including mixing valves are suitable foruse in aspects of the invention. In one aspect, the mixing valvecomprises a globe valve.

The injection of the hydrocarbon solvent into the mixing assembly can beperformed by, for example, a pump; or a pressurized reservoir with aninert gas to raise the pressure higher than the pressure of the causticstream so that the hydrocarbon solvent will flow into the causticstream.

Suitable prefilter assemblies include, for example, PROFILE® filters andPROFILE® II filters, commercially available from Pall Corporation (PortWashington, N.Y.). Prefilter assemblies can have any number of porousprefilter elements, in some aspects, at least two porous prefilterelements, e.g., three or more prefilter elements.

Preferred liquid-liquid coalescer assemblies include those described inU.S. Pat. Nos. 5,443,724 and 5,480,547, U.S. Patent ApplicationPublication 2001/0047967, and EP 0,831,958. Suitable liquid-liquidcoalescer assemblies are commercially available from Pall Corporation(Port Washington, N.Y.). Liquid-liquid coalescer assemblies can have anynumber of liquid-liquid coalescer filter elements (e.g., liquid-liquidcoalescer filter elements in the form of cartridges), typically, atleast two liquid-liquid coalescer filter elements, e.g., three or moreliquid-liquid coalescer filter elements, in some aspects, at least fourfluoropolymer liquid-liquid coalescer filter elements.

Preferably, the coalescer and prefilter cartridges are constructed usingfluoropolymer media such as ethylene chlorotrifluoroethylene (ECTFE) orpolyvinylidene fluoride (PVDF), nylon media, polyphenylene sulfide (PPS)media or other materials compatible with caustic and hydrocarbons andcan contain stainless steel support materials and end caps. The housingsthat hold the prefilters and coalescers can be made from carbon steel orstainless steel.

The following example further illustrates the invention but, of course,should not be construed as in any way limiting its scope.

EXAMPLE

This example demonstrates reducing sulfur from a caustic fluid includingDSO according to an aspect of the invention.

Using the schematic of the system shown in the FIGURE for reference, afirst fluid stream comprising a caustic containing>350 ppmw of DSO and asolid phase is run at 100 gpm, and a low sulfur naphtha hydrocarbonsolvent is injected (using a pump with a flowrate controlled using aflow control valve and a flow meter) into the first fluid stream at aflow rate of 5 gpm (5% of caustic flowrate).

The caustic and solvent are mixed together by passing through a globemixing valve, adjusted to create 15 psid of differential pressuremeasured by the differential pressure gauge (thus creating a shearleading to the creation of fine drops in the micron size range forimproved subsequent coalescence and mass transfer of sulfur from thecaustic phase into the hydrocarbon solvent phase), and the mixture ispassed through a prefilter assembly having two nylon porous depthprefilter cartridges (each 60-inch length by 6-inch diameter) (tradenamePROFILE® filter, Pall Corporation, Port Washington, N.Y.) to remove thesolid phase and start the coalescing process that increases drop sizes,and the mixture, depleted of solid phase, is passed into a horizontallyconfigured liquid—liquid coalescer assembly having four fluoropolymerliquid—liquid coalescer cartridges (each 40-inch length by 3¾-inchdiameter), providing agglomerated emulsified droplets including thesolvent and DSO that coalesce and are more easily separated from thecaustic by buoyancy, and collected from the upper part of theliquid—liquid coalescer assembly in a hydrocarbon sump, that is drainedperiodically as part of a continuous process. The purified caustic(reduced to<180 ppmw of DSO) passes from the lower part of theliquid—liquid coalescer assembly to a mercaptan extractor tower,providing a final product hydrocarbon that reliably maintains low sulfurcontent below the target specification on a continuous basis.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred aspects of this invention are described herein, including thebest mode known to the inventors for carrying out the invention.Variations of those preferred aspects may become apparent to those ofordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The invention claimed is:
 1. A method for purifying a caustic fluidincluding sulfur, the method comprising: (a) mixing the caustic fluidincluding sulfur with a hydrocarbon solvent, including injecting thehydrocarbon solvent, at a pressure greater than a pressure of thecaustic fluid including sulfur, at a rate in the range of 3% to 10% of aflow rate of the caustic fluid including sulfur into a mixing valveoperated at a pressure differential across the mixing valve in the rangeof 10 psid to 50 psid; (b) passing the caustic fluid including sulfurmixed with hydrocarbon solvent at a temperature in the range of from 50°F. to 150° F. through a pre-filter assembly operated at a pressuredifferential in the range of 1 psid to 25 psid, the prefilter assemblycomprising a housing including the inlet and an outlet and defining afluid flow path between the inlet and the outlet with at least oneporous prefilter element in the housing across the fluid flow path,providing a solids-depleted caustic fluid including sulfur mixed withhydrocarbon solvent; (c) passing the solids-depleted caustic fluidincluding sulfur mixed with hydrocarbon solvent at a temperature in therange of from 50° F. to 150° F. through the inlet of a liquid-liquidcoalescer assembly comprising a liquid-liquid coalescer assembly housingincluding the inlet and at least one liquid-liquid coalescer filterelement in the liquid-liquid coalescer assembly housing, theliquid-liquid coalescer assembly housing having an upper part having anupper port, and a lower part having a lower port, wherein theliquid-liquid coalescer assembly is operated at a pressure differentialin the range of 1 psid to 15 psid, with a flow rate in the range of 10gpm to 50 gpm per liquid-liquid coalescer filter element; (i) passingcoalesced droplets comprising sulfur and hydrocarbon solvent through theupper port; and (ii) passing purified caustic fluid having a reducedsulfur content though the lower port.
 2. The method of claim 1, whereinthe caustic fluid including sulfur comprises disulfide oil (DSO).
 3. Themethod of claim 2, wherein (a) includes mixing a caustic fluid includingsulfur having a caustic concentration in the range of 1 degree Baume to10 degrees Baume with the hydrocarbon solvent.
 4. The method of claim 1,comprising a mercaptan removal process.
 5. The method of claim 1,wherein the method is carried out at a system pressure in the range of50 psig to 600 psig.
 6. The method of claim 3, wherein (a) includesmixing a caustic fluid including sulfur having a caustic concentrationin the range of 1 degree Baume to 10 degrees Baume with the hydrocarbonsolvent.
 7. The method of claim 2, comprising a mercaptan removalprocess.
 8. The method of claim 3, comprising a mercaptan removalprocess.
 9. The method of claim 2, wherein the method is carried out ata system pressure in the range of 50 psig to 600 psig.
 10. The method ofclaim 3, wherein the method is carried out at a system pressure in therange of 50 psig to 600 psig.
 11. The method of claim 4, wherein themethod is carried out at a system pressure in the range of 50 psig to600 psig.